The present invention relates to respective methods for cutting a rare earth alloy, manufacturing rare earth alloy plates and manufacturing rare earth alloy magnets with a wire saw, and also relates to a voice coil motor including the rare earth alloy magnet.
A technique of cutting an ingot of silicon with a wire saw to slice the ingot into a large number of wafers is disclosed in Japanese Laid-Open Publication No. 6-8234. In accordance with such a technique, a large number of wafers, each having a constant thickness, can be simultaneously sliced from an ingot by cutting the ingot with a multi-wire running while supplying some slurry containing abrasive grains thereto.
On the other hand, in accordance with a known technique, an ingot of a rare earth alloy is sliced using a rotating dicing blade, for example. However, such a technique using a dicing blade requires an undesirably large cutting margin, because the cutting edge of a dicing blade is thicker than that of a wire. Therefore, such a technique cannot contribute to efficient use of valuable resources. A rare earth alloy is suitable for use as a magnet material, for instance. A magnet has found a wide variety of applications and is now broadly used for various types of electronic appliances. Under the circumstances such as these, it is highly desirable to cut down on the manufacturing cost per a rare earth magnet. And the cost would be considerably reduced if a great number of wafers could be produced simultaneously from an ingot of a rare earth alloy such that a cutting margin can be reduced by the use of a wire saw and that each wafer has a constant thickness.
However, no one has ever reported on successfully cutting a rare earth alloy in accordance with a practical wiresaw technique. The present inventors experimentally cut an ingot of a rare earth alloy with a wire saw. As a result, we found that since a slurry-circulating pipe was clogged up in a very short amount of time with fine powder and grinding debris (i.e., swarf or sludge) involved with wire sawing, no slurry could be supplied to the wire after that, and the wire eventually snapped. If the slurry was entirely replaced every several hours in order to avoid this problem, then wire sawing had to be suspended for a while every time the slurry was replaced. Thus, such machining is not suitable for mass production and it is virtually impossible to put such machining into practice. We also observed that since the sludge was easily deposited in a cutting groove, the cutting resistance noticeably increased and the wire was even more likely to snap as a result. Furthermore, the cutting accuracy was found considerably deteriorated because various unwanted operating failures frequently happened during the cutting process. For example, the wire often disengaged from rollers, around which the wire was wound, because the sludge was also likely to be deposited on the grooves of the rollers. None of these problems has ever been observed during cutting an ingot of silicon or glass in accordance with a conventional wire saw technique.
A prime object of the present invention is providing respective methods for cutting a rare earth alloy and manufacturing rare earth alloy plates with a wire saw to ensure a long-time continuous operation by preventing wire snapping and by drastically reducing the number of times the slurry is replaced.
Another object of the present invention is providing a method for manufacturing rare earth alloy magnets using the method for cutting a rare earth alloy.
Still another object of the present invention is providing a voice coil motor including a rare earth alloy magnet manufactured by the method of the present invention.
A method for cutting a rare earth alloy according to the present invention includes the steps of: a) supplying slurry containing abrasive grains onto a wire; and b) machining the rare earth alloy with the abrasive grains, interposed between the wire and the rare earth alloy, by running and pressing the wire against the rare earth alloy. The slurry contains, as a main component, oil in which the abrasive grains are dispersed, and the viscosity of the slurry at 25xc2x0 C. is in the range from 92 to 175 mPa.sec.
In one embodiment of the present invention, sludge of the rare earth alloy involved with the step b) is separated from the slurry by a magnetic field.
In another embodiment, a magnet separator is used to generate a magnetic field of 0.3 tesla or more in a region through which the sludge is recovered.
In still another embodiment, the running speed of the wire is set in the range from 420 to 760 meters per minute.
In still another embodiment, a wire saw machine is used. The wire saw machine includes: a plurality of rollers rotatably supported, a plurality of ring-shaped grooves being formed on the outer circumference of each said roller at a predetermined pitch; and driving means for rotating the rollers and running the wire wound around the grooves of the rollers.
In still another embodiment, the surface of the outer circumference of each said roller is coated with ester-based urethane rubber.
In still another embodiment, the depth of the grooves of each said roller is set at 0.3 mm or more.
In still another embodiment, the rare earth alloy is cut while the rare earth alloy is lowered downward closer to the running wire.
In still another embodiment, the rare earth alloy is held after the rare earth alloy has been divided into a plurality of blocks, and at least part of the slurry is supplied through a gap between the blocks.
Another method for cutting a rare earth alloy according to the present invention includes the steps of: a) supplying slurry containing abrasive grains onto a wire; and b) machining the rare earth alloy with the abrasive grains, interposed between the wire and the rare earth alloy, by running and pressing the wire against the rare earth alloy. The slurry contains, as a main component, oil in which the abrasive grains are dispersed. And sludge of the rare earth alloy involved with the step b) is separated from the slurry by a magnetic field.
Still another method for cutting a rare earth alloy according to the present invention includes the steps of: a) supplying slurry containing abrasive grains onto a wire; and b) machining the rare earth alloy with the abrasive grains, interposed between the wire and the rare earth alloy, by running and pressing the wire against the rare earth alloy. The slurry contains, as a main component, oil in which the abrasive grains are dispersed. A wire saw machine is used, and includes: a plurality of rollers rotatably supported, a plurality of ring-shaped grooves being formed on the outer circumference of each said roller at a predetermined pitch; and driving means for rotating the rollers and running the wire wound around the grooves of the rollers. And the rare earth alloy is held after the rare earth alloy has been divided into a plurality of blocks, and at least part of the slurry is supplied through a gap between the blocks.
Yet another method for cutting a rare earth alloy according to the present invention includes the steps of: a) supplying slurry containing abrasive grains onto a wire; and b) machining the rare earth alloy with the abrasive grains, interposed between the wire and the rare earth alloy, by running and pressing the wire against the rare earth alloy. The slurry contains, as a main component, oil in which the abrasive grains are dispersed. A wire saw machine is used, and includes: a plurality of rollers rotatably supported, a plurality of ring-shaped grooves being formed on the outer circumference of each said roller at a predetermined pitch; and driving means for rotating the rollers and running the wire wound around the grooves of the rollers. The depth of the grooves of each said roller is set at 0.3 mm or more.
A method for manufacturing rare earth alloy plates according to the present invention includes the steps of: forming an ingot of a rare earth alloy; and separating a plurality of rare earth alloy plates from the ingot of the rare earth alloy. The separating step includes the steps of: supplying slurry containing abrasive grains onto a wire; and machining the ingot with the abrasive grains, interposed between the wire and the ingot, by running and pressing the wire against the ingot. The slurry contains, as a main component, oil in which the abrasive grains are dispersed, and the viscosity of the slurry at 25xc2x0 C. is in the range from 92 to 175 mPa.sec.
A method for manufacturing rare earth alloy magnets according to the present invention includes the steps of: making a sinter out of a rare earth magnetic alloy powder; and separating a plurality of rare earth alloy magnets from the sinter. The separating step includes the steps of: supplying slurry containing abrasive grains onto a wire; and machining the sinter with the abrasive grains, interposed between the wire and the sinter, by running and pressing the wire against the sinter. The slurry contains, as a main component, oil in which the abrasive grains are dispersed, and the viscosity of the slurry at 25xc2x0 C. is in the range from 92 to 175 mPa.sec.
The voice coil motor of the present invention includes a rare earth alloy magnet manufactured by performing the steps of: making a sinter out of a rare earth magnetic alloy powder; and separating a plurality of rare earth alloy magnets from the sinter. The separating step includes the steps of: supplying slurry containing abrasive grains onto a wire; and machining the sinter with the abrasive grains, interposed between the wire and the sinter, by running and pressing the wire against the sinter. The slurry contains, as a main component, oil in which the abrasive grains are dispersed, and the viscosity of the slurry at 25xc2x0 C. is in the range from 92 to 175 mPa.sec.
In one embodiment of the present invention, the thickness of the rare earth alloy magnet is in the range from 0.5 to 3.0 mm.